Make the sausage meatballs by combining the sausage meat with salt and black pepper in a bowl. Form the meat into about 24 small balls.
Add the oil to a large skillet and fry the sausage meatballs until browned all over.
Transfer them to a baking dish, then use the leftover oil to fry the mushrooms and garlic. After the mushrooms have softened, add the can of tomatoes and baby spinach, then continue to cook until the spinach has wilted.
Stir in ½ cup of the shredded cheese, then test for seasoning, adding salt and pepper if necessary. Transfer everything to the baking dish using a slotted spoon, then mix in with the meatballs.
Roast for 15 minutes, then sprinkle the remaining cheese over the top. Continue to bake until the cheese has melted.
Garnish with parsley, if using.
5g net carbs per serving (quarter of recipe, approx 6 meatballs per person)